Noguchi, T¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Faculty of Arts and Science, Kyushu University, Nishi-ku, Fukuoka, Japan

We observed cross sectional ultra-thin sections near the surface of 12 particles recovered from the S-type asteroid Itokawa by the Hayabusa spacecraft in 2010, using spherical aberration–corrected STEM and conventional TEM. Although their mineralogy is almost identical to the equilibrated LL chondrites and therefore basically anhydrous, micrometer-to-submicrometer-sized sylvite was identified on the surface of Itokawa particle RA-QD02-0034. Separately, micrometer-sized halite was also identified on the surface of Itokawa particle RA-QD02-0129. Detailed inspection of the sample processing procedures at the JAXA’s Planetary Materials Sample Curation Facility and textural observation of the sylvite and halite indicate that they were clearly present on two Itokawa particles before they were removed from Clean Chamber #2 at JAXA. However, there is no direct evidence for their extraterrestrial origin at present. If the sylvite and halite are extraterrestrial, their presence suggests that they may be more abundant on the surface of S-type asteroids than previously thought.

Reference
Noguchi et al. (in press) Sylvite and halite on particles recovered from 25143 Itokawa: A preliminary report. Meteoritics & Planetary Science
[doi:10.1111/maps.12333]
Published by arrangement with John Wiley & Sons

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Matija Ćuk^a, Brett J. Gladman^b, David Nesvorný^c

^aCarl Sagan Center, SETI Institute, 189 North Bernardo Avenue, Mountain View, CA 94043
^bDepartment of Physics and Astronomy, University of British Columbia 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
^cSouthwest Research Institute, 1050 Walnut St, Suite 400, Boulder, CO 80302

The Hungaria asteroids are interior to the main asteroid belt, with semimajor axes between 1.8 and 2 AU, low eccentricities and inclinations of 16-35 degrees. Small asteroids in the Hungaria region are dominated by a collisional family associated with (434) Hungaria. The dominant spectral type of the Hungaria group is the E or X-type (Warner et al., 2009), mostly due to the E-type composition of Hungaria and its genetic family. It is widely believed the E-type asteroids are related to the aubrite meteorites, also known as enstatite achondrites (Gaffey et al., 1992). Here we explore the hypothesis that aubrites originate in the Hungaria family. In order to test this connection, we compare model Cosmic Ray Exposure ages from orbital integrations of model meteoroids with those of aubrites. We show that long CRE ages of aubrites (longest among stony meteorite groups) reflect the delivery route of meteoroids from Hungarias to Earth being different than those from main-belt asteroids. We find that the meteoroids from Hungarias predominantly reach Earth by Yarkovsky-drifting across the orbit of Mars, with no assistance from orbital resonances. We conclude that the CRE ages of aubrites are fully consistent with a dominant source at the inner boundary of the Hungaria family at 1.7 AU. From here, meteoroids reach Earth through the Mars-crossing region, with relatively quick delivery times favored due to collisions (with Hungarias and the inner main-belt objects). We find that, after Vesta, (434) Hungaria is the best candidate for an asteroidal source of an achondrite group.

Reference
Ćuk MGladman BJ and Nesvorný D (in press) Hungaria Asteroid Family as the Source of Aubrite Meteorites. Icarus
[doi:10.1016/j.icarus.2014.05.048]
Copyright Elsevier

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Petr Pokorný¹, David Vokrouhlický¹, David Nesvorný², Margaret Campbell-Brown³ and Peter Brown³

¹Institute of Astronomy, Charles University, V Holešovičkách 2, CZ-18000 Prague 8, Czech Republic
²Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
³Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7, Canada

More than a decade of radar operations by the Canadian Meteor Orbit Radar have allowed both young and moderately old streams to be distinguished from the dispersed sporadic background component. The latter has been categorized according to broad radiant regions visible to Earth-based observers into three broad classes: the helion and anti-helion source, the north and south apex sources, and the north and south toroidal sources (and a related arc structure). The first two are populated mainly by dust released from Jupiter-family comets and new comets. Proper modeling of the toroidal sources has not to date been accomplished. Here, we develop a steady-state model for the toroidal source of the sporadic meteoroid complex, compare our model with the available radar measurements, and investigate a contribution of dust particles from our model to the whole population of sporadic meteoroids. We find that the long-term stable part of the toroidal particles is mainly fed by dust released by Halley type (long period) comets (HTCs). Our synthetic model reproduces most of the observed features of the toroidal particles, including the most troublesome low-eccentricity component, which is due to a combination of two effects: particles’ ability to decouple from Jupiter and circularize by the Poynting–Robertson effect, and large collision probability for orbits similar to that of the Earth. Our calibrated model also allows us to estimate the total mass of the HTC-released dust in space and check the flux necessary to maintain the cloud in a steady state.

Reference
Pokorný P, Vokrouhlický D, Nesvorný D, Campbell-Brown M and Brown P (2014) Dynamical model for the toroidal sporadic meteors. The Astrophysical Journal 789:25.
[doi:10.1088/0004-637X/789/1/25]

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